It is narrated from Sayyiduna Abu Sa'id al-Khudri (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "There is no sadaqah on fewer than five camels, there is no sadaqah on fewer than five awqiyah, and no sadaqah will be taken on less than five wasq either."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قسم الصدقات / 13123